Chapter 9

Where does the citric acid cycle occur in eukaryotes? a. in the cytosol of cells b. in the intermembrane space of mitochondria c. in the inner membrane of mitochondria d. in the matrix of mitochondria

What does the chemiosmotic hypothesis claim? a. ATP is generated using phosphates taken from intermediates in the electron transport chain. b. ATP is generated using a phosphate gradient produced by glycoly- sis and the citric acid cycle. c. ATP is generated using a proton-motive force that is produced by the electron transport chain. d. Water is generated using electrons taken from NADH and FADH and transported through the electron transport chain.

After glucose is fully oxidized by glycolysis, pyruvate processing, and the citric acid cycle, where is most of its energy stored?

What is the primary function of the reactions that follow glycolysis in a fermentation pathway? a. to regenerate \(\mathrm{NAD}^{+}\) from NADH, so glycolysis can continue b. to synthesize pyruvate from lactate c. to regenerate NADH from \(\mathrm{NAD}^{+}\), so electrons can be donated to the electron transport chain d. to synthesize electron acceptors, so that cellular respiration can continue

Compare and contrast substrate-level phosphorylation and oxidative phosphorylation.

If you were to expose cells that are undergoing aerobic cellular respiration to a radioactive oxygen isotope in the form of \(\mathrm{O}_{2}\), which of the following molecules would you expect to be radiolabeled? a. pyruvate b. water c. \(\mathrm{NADH}\) d. \(\mathrm{CO}_{2}\)

In step 3 of the citric acid cycle, the enzyme isocitrate dehydrogenase is regulated by NADH. Compare and contrast the regulation of this enzyme with the regulation of phosphofructokinase in glycolysis.

Cyanide \(\left(\mathrm{C} \equiv \mathrm{N}^{-}\right)\) blocks complex IV of the electron transport chain. Suggest a hypothesis for what happens to the ETC when complex IV stops working. Your hypothesis should explain why cyanide poisoning in humans is fatal.

Early estimates suggested that the oxidation of glucose via aerobic respiration would produce 38 ATP. Based on what you know of the theoretical yields of ATP from each step, show how this total was determined. Why do biologists now think this amount of ATP/glucose is not achieved in cells?

Research has shown that cellular damage associated with aging occurs via the formation of oxygen radicals called reactive oxygen species (ROS). These radicals are produced when an excessive proton gradient across the inner mitochondrial membrane slows down the rate of electron transport in the ETC. Propose a hypothesis to explain how a proton gradient can reduce the rate of electron transport.

In the above study, the investigators determined that a low concentration of DNP increased the average life span from 719 days (Control) to 770 days (DNP). If the U.S. population has an average life span of 79 years, then how many years would be added if the same percentage increase were observed?

How could you determine if the mitochondrial ETC is affected in DNP-treated mice? Propose an experiment to determine if there is a correlation between life span and ETC activity in mitochondria isolated from mice used in the experiment above.

In addition to an increased life span, mice treated with low concentrations of DNP also showed a significantly lower weight gain compared to the control group despite no difference in the amount or type of food ingested. Propose an explanation for why DNP would have this effect.

In the 1930 s, DNP was introduced as a diet drug until it was banned from human use because of adverse side effects when high concentrations of the drug were used. These included increased respiration and even death. Propose an explanation for the side effects based on the effect DNP has on the proton gradient.